The invention relates to gas turbine engines. More particularly, the invention relates to gas turbine engine compressor vanes.
A gas turbine engine typically includes one or more rotor stacks associated with one or more sections of the engine. A rotor stack may include several longitudinally spaced apart blade-carrying disks of successive stages of the section. A stator structure may include circumferential stages of vanes longitudinally interspersed with the rotor disks. The rotor disks are secured to each other against relative rotation and the rotor stack is secured against rotation relative to other components on its common spool (e.g., the low and high speed/pressure spools of the engine).
Numerous systems have been used to tie rotor disks together. In an exemplary center-tie system, the disks are held longitudinally spaced from each other by sleeve-like spacers. The spacers may be unitarily formed with one or both adjacent disks. However, some spacers are often separate from at least one of the adjacent pair of disks and may engage that disk via an interference fit and/or a keying arrangement. The interference fit or keying arrangement may require the maintenance of a longitudinal compressive force across the disk stack so as to maintain the engagement. The compressive force may be obtained by securing opposite ends of the stack to a central shaft passing within the stack. The stack may be mounted to the shaft with a longitudinal precompression force so that a tensile force of equal magnitude is transmitted through the portion of the shaft within the stack.
Alternate configurations involve the use of an array of circumferentially-spaced tie rods extending through web portions of the rotor disks to tie the disks together. In such systems, the associated spool may lack a shaft portion passing within the rotor. Rather, separate shaft segments may extend longitudinally outward from one or both ends of the rotor stack.
Desired improvements in efficiency and output have greatly driven developments in turbine engine configurations. Efficiency may include both performance efficiency and manufacturing efficiency.
Interstage sealing has been one area of traditional concern. Traditional sealing systems utilize abradable seal material carried on inboard vane platforms and interacting with knife edge runners on one or both of the adjacent blade platforms or on connecting structure.
U.S. patent application Ser. Nos. 10/825,255, 10/825,256, and 10/985,863 of Suciu and Norris (hereafter the Suciu et al. applications, disclosures of which are incorporated by reference herein as if set forth at length) disclose engines having one or more outwardly concave interdisk spacers. With the rotor rotating, a centrifugal action may maintain longitudinal rotor compression and engagement between a spacer and at least one of the adjacent disks. The '255 and '256 applications show knife edge sealing runners on the spacers whereas the '863 application shows inboard free tips on vane airfoils in close running proximity to the spacers.